Circuit interrupters currently employed within industrial electrical distribution systems include separable contacts arranged for interrupting circuit current on command from an electronic trip unit. Current transducers such as current transformers as described within U.S. Pat. No. 4,672,501 entitled "Circuit Breaker and Protective Relay Unit" are often used to provide the trip unit with sample indication of circuit current. Such current transformers require space within the circuit breaker enclosure and increase in size with respect to the circuit breaker ampere rating. The increased size results in an increase in the size of the circuit breakers used in higher ampere-rated applications.
Hall effect devices such as described in U.S. Pat. No. 5,615,075 entitled "AC/DC Current Sensor for a Circuit Breaker" are much smaller in size than current transformers and allow for reduced space within the circuit breaker enclosure. Such Hall effect devices require some sort of a magnetic flux enhancer or concentrator to increase the Hall effect response at a further increase in the overall cost of the circuit breaker components.
An additional problem with use of Hall effect devices, particularly within multi-phase circuits, is the sensitivity of the Hall effect device to the magnet flux developed within adjoining phases. An overcurrent occurrence within one phase, for example, could generate substantial magnetic flux to increase the sensitivity of the Hall effect device in an immediately adjacent phase resulting in a false indication of an overcurrent occurrence in the adjacent phase.
The purpose of the invention is to describe an arrangement whereby Hall effect devices can be used with multi-pole circuit breakers without incurring cost increases over standard current transformers and without being subject to interphasal magnetic conditions.